Profile

I am interested in the processes that govern ecological communities, the interplay between community and ecosystem-level processes, and the interactions between the global biosphere and climate. My approach is to develop, calibrate and test mathematical models that explain ecological structure and function.
Currently I direct the Princeton Environmental Institute and co-direct Princeton's Carbon Mitigation Initiative. My research focusses on all aspects of the global carbon cycle. The group is composed of ecologists, physical and biological oceanographers, and atmospheric scientists, and investigates issues ranging from the effects of global vegetation on climate, to the large-scale measurement of natural and anthropogenic greenhouse gas emissions.
I am now working most intensively on a new model of the terrestrial biosphere. Over the past several years, we have developed methods to scale-up individual based models of communities and ecosystems. We use these methods to scale up so called gap models of vegetation. The method provides partial differential equations that govern the behavior of a large scale simulation model of a landscape, without the need to run the individual-based model. Our global model makes predictions about the large-scale distribution of biomes and associated biogeochemical fluxes, as well as specific local predictions including hourly physiological carbon gain and water loss, community composition and dynamics throughout succession, the outcome of spatial competition among plant species, and the fluxes of nitrogen, water and carbon.
Because the model is based on measurable properties of individuals and local-scale processes, the work provide sample opportunities for field studies to calibrate and test it. We are currently working on field projects in Amazonia and the deciduous-evergreen ecotone in the northern Midwest. We are also continuing the theoretical studies of ecological scaling rules, and are coupling the global ecosystem model to regional and global models of atmosphere and oceans.
During the next several years, my research will focus on the following questions. How and to what extent the terrestrial biosphere affects climate? Does the feedback between climate and vegetation lead to multiple stable states of climate? If so, could human land use cause a flip to an alternative state (we are most concerned currently by the possibility of a dry tropics caused by deforestation)? How does biodiversity affect global ecosystem function?